In semiautomatic or automatic firearms, the cartridges which are fired are commonly stored in a detachable magazine. The magazine defines an enclosure adapted to contain at least one column of cartridges. The cartridges are loaded into the magazine so as to be located atop a magazine follower which engages a lowermost cartridge in the magazine. A magazine spring is included in the magazine and is compressible between the magazine follower and a bottom portion of the magazine so as to bias the follower and loaded cartridges upwardly in the magazine toward an upper open end. An uppermost cartridge from the magazine is loaded into a firing position in the firearm by cooperation with a slide of the firearm. The slide is adapted to be moveable from an initial firing position rearwardly with respect to the firearm frame, barrel, and magazine and then return forwardly under a spring biasing force. During the returning forward movement of the slide, the slide contacts and strips the uppermost cartridge from the magazine. Under the contact from the slide and the biasing force from the magazine spring, the cartridge moves upwardly with respect to the magazine and forwardly in the firearm, ultimately reaching a firing position in the firing chamber of the firearm. When a loaded magazine is first placed in the firearm, the slide may be manually cycled to place the first cartridge from the magazine in the firing position. Thereafter, energy from the fired cartridge is used to cycle the slide to eject the casing of the fired cartridge and load the next cartridge from the magazine into the firing chamber. In this manner, each successive shot fired causes the magazine follower and the column of cartridges to incrementally travel upwardly, and each successive cartridge is fed into the firing position in the firearm until no further cartridges remain in the magazine.
A firearm may be designed so that when the last cartridge from the magazine is fired and the magazine is thus empty, the slide locks open and does not complete its full cycle of movement. This slide locking gives the operator an important visual indication that the magazine is empty. This visual indication provided by the slide locking in an open position is extremely important in a combat, law enforcement, or personal defense setting in which it is not practical for the operator to keep track of the number of cartridges they have fired from a given magazine. The locked open slide informs the operator that they must take cover and reload.
The slide stop mechanism for locking the slide in the open position when the magazine is empty may include a lever mounted on the firearm frame. This slide stop lever is mounted so that it may move between a locking position in which it catches on a notch or other feature of the slide, and a retracted position in which the slide is free to cycle. The slide stop lever may be biased in some fashion to the retracted position, and, in some firearms, is moved to the locking position by contact with a portion of the magazine follower. In particular, the slide stop lever may include or be connected to a slide stop lug which extends through an opening in the firearm frame into the area of the firearm that receives the upper end of the magazine. As the last cartridge is stripped from the magazine, the follower reaches its uppermost position in the magazine under the biasing force of the magazine spring. At this point, contact between a portion of the follower and the slide stop lug forces the slide stop lever toward its extended, locking position. Then, when the last cartridge from the magazine is fired, the slide moves rearwardly under the force of the discharge but is caught in the open position by contact between the slide stop lever and the notch or other locking feature on the slide.
Several different types of magazine followers have been developed for firearms in which the follower is used to actuate the slide stop, each having a somewhat different structure for contacting the slide stop lug so as to move the slide stop lever to the extended, locking position. Molded plastic followers include a base part with a guide skirt that commonly depends from the base part around its entire periphery. The upper end of the magazine spring is adapted to fit into the recess formed by the skirt. These molded plastic followers require a cutout at a front end of the base and skirt structure to produce a slide stop actuating surface below the plane of the base part. This cutout area and slide stop actuating surface must be below the plane of the base part because the base part would otherwise contact the slide stop lug and actuate the slide stop prematurely while the last cartridge remained in the magazine. U.S. Pat. No. 7,047,686 shows a molded plastic follower having a cutout area and a slide stop actuating surface below the plane of the base part.
A second type of follower, usually made from a thin plate or sheet of metal, includes a base part and a part that is cut and bent relative to the base to provide a stair-step like structure. This stair-step like structure provides a slide stop actuating surface which is located well below the plane of the follower base part similarly to the slide stop actuating surface of the molded plastic follower. This positioning below the plane of the follower base part is again required in order to prevent premature actuation of the slide stop while the last cartridge remains in the magazine. U.S. Pat. No. 2,944,357 provides an example of this stair-step like follower.
A third type of follower is shown in U.S. Pat. No. 4,446,645. This type of follower includes a spring action built in to the follower itself and will be referred to herein as a spring-action follower. The spring-action follower shown in U.S. Pat. No. 4,446,645 includes a base part, a rear guide, and a cartridge engaging part that forms a leaf spring with respect to the base part. The cartridge engaging part provides additional spring action to bias the cartridges upwardly in the magazine and allows the magazine to use a weaker magazine spring. This weaker magazine spring may be compressed into a smaller fully compressed position and the cartridge engaging part may be compressed to allow at least one additional cartridge to be held in the magazine without changing the length of the magazine. As shown particularly in FIGS. 1 and 2 of U.S. Pat. No. 4,446,645, a finger portion is located at a front end of the base part. This finger portion provides a slide stop actuating surface for the follower.